prf_ssl3.cpp

Go to the documentation of this file.

/*
* SSLv3 PRF
* (C) 2004-2006 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
 
#include <botan/prf_ssl3.h>
#include <botan/symkey.h>
#include <botan/exceptn.h>
#include <botan/sha160.h>
#include <botan/md5.h>
#include <botan/internal/assert.h>
#include <memory>
 
namespace Botan {
 
namespace {
 
/*
* Return the next inner hash
*/
OctetString next_hash(size_t where, size_t want,
                      HashFunction& md5, HashFunction& sha1,
                      const byte secret[], size_t secret_len,
                      const byte seed[], size_t seed_len)
   {
   BOTAN_ASSERT(want <= md5.output_length(), "Desired output too large");
 
   const byte ASCII_A_CHAR = 0x41;
 
   for(size_t j = 0; j != where + 1; j++)
     sha1.update(static_cast<byte>(ASCII_A_CHAR + where));
   sha1.update(secret, secret_len);
   sha1.update(seed, seed_len);
   SecureVector<byte> sha1_hash = sha1.final();
 
   md5.update(secret, secret_len);
   md5.update(sha1_hash);
   SecureVector<byte> md5_hash = md5.final();
 
   return OctetString(&md5_hash[0], want);
   }
 
}
 
/*
* SSL3 PRF
*/
SecureVector<byte> SSL3_PRF::derive(size_t key_len,
                                    const byte secret[], size_t secret_len,
                                    const byte seed[], size_t seed_len) const
   {
   if(key_len > 416)
      throw Invalid_Argument("SSL3_PRF: Requested key length is too large");
 
   MD5 md5;
   SHA_160 sha1;
 
   OctetString output;
 
   int counter = 0;
   while(key_len)
      {
      const size_t produce = std::min<size_t>(key_len, md5.output_length());
 
      output = output + next_hash(counter++, produce, md5, sha1,
                                  secret, secret_len, seed, seed_len);
 
      key_len -= produce;
      }
 
   return output.bits_of();
   }
 
}